In the devices currently in use, between the different manufacturing stages the substrates are transported and stored at atmospheric pressure in the transport cases that protect them from particular pollution present in the atmosphere of clean rooms. A transport case comprises a leak proof peripheral wall with an entry-exit opening capable of being closed by a casing door fitted with leak prevention means. The substrates take, in particular, the form of square masks or of circular shape slices in a semi-conductor material such as silicon. In a transport case, the substrates are stacked close to one another in a kind of rack also referred to as cassettes or baskets.
Currently, a first type of transport case is used, designated by the acronym SMIF (for “Standardized Mechanical Interface”). These transport cases comprise a bell shaped casing body resting on a base plate that closes their bottom opening, constituting a door. The basket is generally set or held on the base plate. The substrates are stacked horizontally in the basket.
A second type of transport case is used, designated by the acronym FOUP (for “Front Opening Unified Pod”) is also used, which comprises a lateral opening casing body.
The transport cases must be capable of being connected with entry/exit interfaces of semiconductor component manufacturing or substrate processing facilities. The transport cases are coupled with the equipment via means ensuring permanent air tightness in regard to the external atmosphere in the clean room.
The interface is a system enabling positioning of the transport case, opening of its case door, and the grasping and transport of the substrate for transfer between the transport case and the equipment. The said interface, sometimes also called mini-environment, shall hereafter be referred to by the term “frontal equipment module”, or, simply module, and by the acronym EFEM (for Equipment Front End Module).
Under atmospheric pressure, the EFEM module comprises robotic means to transport each substrate from the transport to a loading and unloading chamber (designated by the term “load lock”) that communicates with a transfer chamber preceding a process chamber. During the loading process, the substrates are transferred from the transport case to the lock under atmospheric pressure. The loading lock is then subjected to very low pressure. Then the transfer chamber robot transports the substrate from the load lock to the vacuum processing chamber, where processing takes place. When processing is completed, the reverse operation—unloading of the substrate from the processing chamber to the transport case—requires bringing the load lock back to atmospheric pressure before transfer of the substrate with the help of robotic means to the EFEM module and the transport case.
These gas pressure variations require pumping and re-pressurizing to atmospheric pressure operations that cause gas flows likely to generate particulate contaminations of the loading lock and therefore of the substrates. It is therefor particularly necessary to limit possible contaminations, so as to increase the productivity of semiconductor manufacturing facilities. Best efforts are therefore devoted to minimizing oxidation and corrosion phenomena affecting the substrates during the processing phases, the waiting phases in the transport case between two steps of the process, or the transfer phases from one semiconductor processing equipment to another.
One solution is to implement purging solutions at the end of the processing, but for certain new technologies the oxidation or corrosion phenomena take place even before the end of the processing of complete lots of substrates. This forces manufacturers to divide the lots and to process each portion successively, which leads to an increase in the total lot processing time.
Another solution consists in reducing the waiting phases between two steps of the process, but this requires increasing the quantity of equipment and raises cost issues.